Some types of vehicles installed with an engine automatic stop-and-start system, such as an idle reduction control system, have been recently developed for reduction in fuel cost, in exhaust emission, and the like. Such engine automatic stop-and-start systems, an example of which is disclosed in Japanese Patent Application Publication No. 2002-122059, are designed to automatically stop an internal combustion engine installed in a vehicle in response to a driver's engine stop request. After the stop of the internal combustion engine, these engine automatic stop-and-start systems are designed to cause, in response to a driver's operation to restart the vehicle, a starter to crank the internal combustion engine, thus restarting the internal combustion engine.
In normal starters, a pinion is shifted by an actuator toward a ring gear coupled to a crankshaft of an internal combustion engine to be engaged with the ring gear. While being meshed with the ring gear, the pinion is rotatably driven by a motor so that the crankshaft is rotated. This cranks the internal combustion engine.
Such an engine stop-and-start system is designed to, during the internal combustion engine being decelerated in response to a driver's engine stop request, when an engine restart request occurs, wait until the engine speed becomes nearly zero, and thereafter cause the starter to crank the internal combustion engine. For this reason, a substantial amount of time has elapsed since the occurrence of the engine restart request before the restart of the internal combustion engine. The elapsed time may cause the driver to feel that the restart of the internal combustion engine is delayed.
In order to address this problem, each of Japanese Patent Application Publications No. 2005-330813 and 2002-70699 discloses an engine stop-and-start system. The disclosed engine stop-and-start system is designed to, during the internal combustion engine being decelerated in response to a driver's engine stop request, when an engine restart request occurs, synchronize a rotational speed of the pinion with that of the ring gear, and thereafter engage the pinion with the ring gear to thereby cause the starter to crank the internal combustion engine.
However, the engine stop-and-start system disclosed in the Patent Application Publications No. 2005-330813 and 2002-70699 is designed to carry out the synchronization of the rotational speed of the pinion with that of the ring gear and the engagement of the pinion with the ring gear independently of: a value of the rotational speed of the internal combustion engine at the moment when the engine restart request occurs; and the behavior of the engine speed (rotational speed of the ring gear) after the occurrence of the engine automatic stop request. This, depending on at least one of the value of the rotational speed of the ring gear at the occurrence of the engine restart request and the behavior of the engine speed after the occurrence of the engine automatic stop request, may increase noises due to the engagement of the pinion with the ring gear.